Vibratory separators use a screen assembly to sort “oversized” particles from fluid or other particles. The screen assembly includes a wire or synthetic mesh screen material that is stretched across a frame. The frame has an interior edge that contacts the screen material. Product to be separated is introduced to the top surface of the screen material and the screen assembly is vibrated by the vibratory separator. Individual wires in the screen material near the edge of the frame are strained by the weight of the product to be separated. Additionally, the individual wires are further strained by the vibration of the frame. The strain on each individual wire varies around the interior edge of the frame. Once one of the individual wires breaks under the strain, nearby individual wires are placed under greater strain. The damage to the screen material often widens across several individual wires.
The frame is made of steel, thermoset or rigid composite thermoplastic. The screen material is attached to a steel frame by spot welding or by using an adhesive. The screen material is attached to a thermoset frame by using an adhesive. For either attachment method, strain relief is provided at the interface of the screen material and the interior edge of the frame. A bead of silicone or other caulking-type of elastomer bead is manually applied to the frame to provide strain relief to the screen material.
The screen material is attached to rigid composite thermoplastic frames by heating the thermoplastic material and then pressing the mesh into the soft thermoplastic, which is then allowed to cool. Existing composite frame includes an internal mesh support grid that utilizes valuable sorting area, leaving less area for processing.
Improved screen assemblies having a rigid support section formed from a polymeric material and a cushioned strain relief zone have been proposed. See U.S. Pat. No. 7,249,677. In the prior screen assembly, the cushioned strain relief zone extends along an inner peripheral wall of the rigid support section around an opening to provide a cushioned support to the edge of a screen cloth extending across the opening. The rigid support section and the cushioned strain relief zone are made of different materials. Each material has a different hardness. In particular, the material forming the rigid support section is harder than the material forming the strain relief zone.